Brazil’s unique fishing collaboration between dolphins and humans may be disappearing, scientists warn

A unique, century-old collaboration between humans and dolphins in Brazil, which has seen the two species team up to fish together, may be under threat of disappearing, according to a new study.

The research, published following 15 years of study on Monday in the journal PNAS, has documented this rare example of collaboration between the two top predator species that has been beneficial to both parties for nearly 150 years and called for new conservation strategies to protect the practice.

“We knew that the fishers were observing the dolphins’ behavior to determine when to cast their nets, but we didn’t know if the dolphins were actively coordinating their behaviour with the fishers,” study co-author Mauricio Cantor from the Oregon State University in the US said in a statement.

Scientists used drones and underwater imaging to observe the behaviours of fishers and dolphins with unprecedented detail.

They found that both humans and dolphins could catch more fish by working in synchrony.

Dolphins herd schools of mullet towards the coast which increase the availability of these fishes within the reach of the net-casting fishers, the study found.

The cooperation also benefits the dolphins, scientists say, adding that the animals that engaged in cooperative fishing in the area have an over 10 per cent increase in survival rates.

“When dolphins approach the fishers’ nets closely and cue fishers in, they dive for longer and modify their active foraging echolocation to match the time it takes for nets to sink and close over mullets – but only when fishers respond to their foraging cues appropriately,” scientists wrote in the study.

“This shows that this is a mutually beneficial interaction between the humans and the dolphins,” Dr Cantor said.

While it is common to see synchronized movements of flocks of birds and schools of fish – collaborative behaviour that can be key to the survival of the animals involved – such behaviour in predators on top of the food chain such the Lahille’s bottlenose dolphins and the traditional net-casting fishers in Brazil is much rarer, researchers say.

This team-up has been widely documented in the city of Laguna on Brazil’s southern coast, where the cultural tradition has been followed for over 140 years and has also been passed down through generations of fishers and dolphins.

The collaboration is also specific to this population of dolphins, scientists say, adding that it is not a genetic trait in the animals.

Such synchrony between species has been documented in a handful of locations elsewhere in the world, and is also in decline or has disappeared completely in most places, researchers say.

Due to its rarity, the cultural practice between the fishers and dolphins in Brazil is being considered for a cultural heritage designation, Dr Cantor said.

“From the fishers’ perspective, this practice is part of the culture of the community in all kinds of ways. They acquire skills passed down from other fishers and knowledge is spread through social learning. They also feel connected to this place and have a sense of belonging to the community,” he explained.

Scientists also ran a predictive model which suggests the practice could be threatened if populations of mullet – the type of fish both dolphins and people are seeking – continue to decline, or if future generations of fishers lose interest in learning the art of this unique fishing practice.

“The practice is unlikely to continue if either the dolphins or the fishers no longer benefit from it,” Damien Farine, another author of the study from the University of Zurich in Switzerland said.

Scientists say there may already be early signs of decline in the practice.

“If we take steps to document and conserve the knowledge and the culture of the practice, we can indirectly and positively impact the biological aspects, as well,” Dr Farine said.

Since most interactions between species documented across the world are mainly competitive than mutually beneficial, researchers say the new research can lead to a better understanding of the conditions such interspecies cooperation can evolve.

They believe the findings are of “growing importance” in a rapidly changing world to also unravel under what conditions such cooperation might go extinct, “or flip from a cooperative to a competitive interaction.”

Scientists call for urgent conservation action to ensure the future of this practice in Brazil where both the dolphins and the fishers are reliant on a strong and healthy fish population for the cooperative relationship to succeed.

In recent years, they say, the region has seen reduced availability of fish as well as reduced interest among the fishers in learning the tradition.

They say conservation strategies like understanding the main reasons for the local fish decline, reducing the use of illegal nets, as well as incentives to encourage the traditional practice may go a long way.

“We don’t know what is going to happen in the future, but our best guess, using our best data and best models, is that if things keep going the way they are right now, there will be a time when the interaction will no longer be of interest by at least one of the predators,” Fábio Daura-Jorge, study author from Brazil’s Universidade Federal de Santa Catarina, said.

“This phenomenon of mutually-beneficial interaction between wildlife and humans is getting more and more rare and seems to be at global risk. The cultural value and the biological diversity are important, and it’s important to preserve it,” Dr Cantor added.